Bio-battery could power medical implants

WASHINGTON – Researchers said they have demonstrated that the inner ear of mammals can be used as natural battery to power implanted electronic devices.

The focus of the research is a chamber in the inner ear filled with ions that produces an electrical potential to drive neural signals. Researchers from MIT, Harvard University and the Harvard-MIT Division of Health Services said they have demonstrated the biological battery’s potential for powering devices implanted in the ear without impairing hearing.

One application could be monitoring biological activity in the ears of patients with hearing or balance impairments. Eventually, the researchers said, the implant could be used to deliver medicines and therapies.

“We have known for 60 years that this battery exists and that it’s really important for normal hearing, but nobody has attempted to use this battery to power useful electronics,” said Konstantina Stankovic, a surgeon at the Massachusetts Eye and Ear Infirmary. Stankovic and graduate student Andrew Lysaght implanted electrodes in the ears of guinea pigs. Low power monitoring devices were attached to the electrodes. The devices were able to wirelessly transmit data about the chemical condition of the ear to an external receiver.

The ear converts the vibration of the eardrum into electromechanical signals that are processed by the brain. The biological battery is the source of individual signal’s current. The chamber is located in the part of the ear called the cochlea. Some of the cells in the membrane that divides the chamber are specialized to pump ions. An imbalance of potassium and sodium ions on opposite sides of the membrane helps create and electrical voltage.

To avoid the disruption of hearing, a device powered by the biological battery can harvest only a small fraction of its power, the researchers noted. Hence, ultra-low-power chips needed to operate the implants were developed by MIT’s Microsystems Technology Laboratory (MTL). The chip control circuit was drastically simplified to reduce the device’s power consumption.

The device was initially kick-started, said MTL’s Anantha Chandrakasan. “Once we do that, we can be self-sustaining. The control runs off the output.”

The results of the research were reported in the current issue of the journal Nature Biotechnology.